A massive study just debunked a pervasive myth about male and female brains

For centuries, people have clung to the belief that there's
something inherently different between the male brain and the
female brain.

But in a new study, scientists combed through the brain scans of
more than 1,400 people, and found that while there are some
distinct brain differences between men and women, there's no such
thing as a distinctly "male" or "female" brain.

"Our study demonstrates that, although there are sex/gender
differences in the brain, human brains do not belong to one of
two distinct categories: male brain/female brain," the
researchers wrote in the study,
which was published November 30 in the journal Proceedings
of the National Academy of Sciences.

'Male' and 'female' brains

It has long been assumed that men and women have different
brains.

And some previous research had supported that notion,
finding some differences in the structure of male and female
brains. A 2014 study of
949 people found that men's brains had more connections within
each brain hemisphere, whereas women's brains had more between
connections between hemispheres.

But otherresearch had
defied the notion that human brains can be divided into simple
"male" and "female" categories.

To get at an answer, Daphna Joel, a psychologist at Israel's
Tel-Aviv University, and her colleagues analyzed MRIs scans from
four separate studies comprising a total of more than 1,400
people.

The researchers scored the study participants on a number of
variables like personality traits, relationships, activities, and
attitudes. Then, they took traits that were more
commonly seen in a subset of men or women, and
defined male/female categories based on scores
for those traits. They also had a category classified as
"intermediate" for those who scored somewhere in between.

Next, the researchers determined whether each brain fit
into one of their three categories: male, female, or
intermediate. If it didn't, meaning it had at least one
trait at the "female end" and one trait at the "male end,"
it was said to show "substantial variability."

A mental mosaic

The differences between male and female brains were minimal, the
researchers found. Depending on the data set, between a
quarter and more than half of the brains they studied showed
substantial variability. In comparison, 8% of
brains or fewer fit neatly into the categories.

This graphic shows the volumes of brain regions in 42 adults,
revealing how much overlap there is between male and female
brains (green = large, yellow = small):Image courtesy of Zohar Berman and Daphna
Joel

The fact that there was so much overlap between characteristics
of "male" and "female" brains suggests that most people don't fit
into one of these two categories.

Instead, the researchers wrote, each brain "is a unique mosaic of
features, some of which may be more common in females compared
with males, others may be more common in males compared with
females, and still others may be common in both females and
males."

Margaret McCarthy, a neuroscientist at the University of
Maryland who was not involved with the study,
said it offered the first
strong evidence that there's no such thing as a male or
female brain. That's not to say there are no
sex differences in the brain, but these differences are not
uniformly different in any one individual, she told
Business Insider in an email.

Like any study, of course, this one has its weaknesses as
well. For one, it looked at patterns of brain connectivity,
but did not connect those patterns to behavior,
McCarthy pointed out. In other words, we won't know
whether people whose brains fit mostly in the
masculine or feminine zones also act typically masculine or
feminine.